The present invention relates to an improvement of a speed control apparatus for elevator system.
A speed of a cage in an elevator system is controlled through a long main rope as well-known. It is necessary to stabilize a control system including the main rope system. Various improvements have been proposed for the purpose. FIG. 1 shows one of the conventional system comprising an acceleration feedback circuit.
In FIG. 1, the reference numeral (1) designates a speed command generator; (2) designates a speed control amplifier; (3) designates an acceleration control amplifier; (4) designates a current control amplifier; (5) to (7) respectively designate adders; (8) designates a thyristor converter; (9) designates an armature of a DC motor connected to the thyristor converter (8); (10) designates a shunt winding; (11) designates a DC power source; (12) designates a detector for current of the armature; (13) designates a speed tachometer driven by the armature (9); (13a) designates a speed signal as the output of said speed tachometer; (14) designates an acceleration feedback circuit; (14a) designates an acceleration signal as the output of said acceleration feedback circuit; (15) designates a suspension sheave; (16) designates a deflector sheave; (17) designates a main rope; (18) designates a cage; and (19) designates a counterweight.
The elevator system comprises the speed feedback circuit, the acceleration feedback circuit (14) and the current feedback circuit which control the thyristor converter (8). A DC variable voltage is applied to the armature (9) and the speed of the cage (18) connected to the armature (9) is controlled depending upon the command of the speed command generator (1).
It has been proposed, in said structure, to give a transfer characteristic constant of the acceleration feedback circuit (14) as the following equation in order to inhibit a vibration of the control system by the resonance phenomenon in the main rope system. ##EQU1## wherein G designates a transfer characteristic constant; K designates a gain; S designates Laplace's operator; .omega..sub.1 and .omega..sub.2 designate angular velocities.
The angular velocities .omega..sub.1, .omega..sub.2 are selected as follows. EQU .omega..sub.1 &lt;.omega..sub.r &lt;.omega..sub.2 ( 2)
wherein .omega..sub.r designates an angular velocity corresponding to the resonance frequency of the main rope system.
The control system can be easily stabilized by said structure.
On the other hand, various disturbances for causing vertical vibration of the cage (18) are found in the control system for the elevator. PG,4 For example, sometimes a motor has torque ripple. The frequency of the torque ripple is proportional to the speed of the cage. When the frequency corresponds to the resonance frequency of the main rope, the cape is vibrated by the torque ripple amplified by the main rope at this speed. This condition is shown in FIG. 2, wherein V.sub.0 designates a speed of the cage under corresponding the frequency of the torque ripple of the motor to the resonance frequency of the main rope.
FIG. 2(a) shows the speed of the cage and (b) shows the acceleration waveform of the cage.
The vibration of the cage in the practical operation is started at the speed V.sub.1 (which is slightly lower than V.sub.0) and is attenuated at the speed V.sub.2 (which is slightly higher than V.sub.0).
The acceleration feedback circuit imparts the function for stabilizing the speed control system including the main rope and also imparts attenuation of vibration caused by said outer disturbance. The gain K in the equation (1) for lowering the vibration of the cage by the outer disturbance should be remarkably larger than the gain for stabilizing the system. When the gain is too large, the following disadvantages are caused. Therefore, it has not been attained to decrease the vibration caused by the torque ripple by increasing this gain. That is, the ripple of the tachogenerator is amplified by increasing the gain whereby the cage is vibrated by the ripple of the tachogenerator at the speed V.sub.0 .spsb.' (which is different from V.sub.0). In order to prevent such trouble, it has been required to use the expensive low ripple tachogenerator and the driving device thereof. The speed V.sub.0.spsb.' is the speed of the cage under corresponding the ripple frequency of the tachogenerator to the resonance frequency of the main rope.